In recent years, solid-state light illuminators, such as LASERs and light-emitting-diodes (LEDs), and other narrow-banded light illuminators capable of producing phase-coherent light, such as wavelength specific plasma lamps, have drawn significant attention as alternative light sources to traditional light sources, such as arc lamps, for use in imaging systems, especially imaging systems employing light valves, due to many advantages, such as compact size, greater durability, longer operating life, and lower power consumption.
Regardless of the widely embraced superior properties of solid-state illuminators over traditional light sources, it is however difficult to optically couple solid-state illuminators with light valves. For example, it is difficult to generate a far-field illumination area with uniform illumination intensity at the light valve location using solid-state or narrow-banded light illuminators because the illumination light from the solid-state illuminators and most narrow-banded illuminators are highly collimated as compared to the light from traditional illuminators. Some existing applications of solid-state and/or narrow-banded light illuminators in imaging systems that employ light valves involve optics, such as diffusers, lenses, and other optical elements for producing appropriate far-field illumination areas at the light valve locations, and directing the highly collimated light onto and from the light valves of the imaging systems. These optical elements, as well as their optical arrangements, occupy a large amount of spaces in imaging systems, which in turn, dramatically limit reduction of imaging system sizes in forming compact and portable imaging systems. Moreover, these optical elements increase costs of the imaging system and complicate imaging system design and manufacture.
Another approach to optically couple solid-state or narrow-banded illuminators to light valves in imaging systems is to use holographic optical elements (HOE) and/or other types of optically diffractive elements. A holographic optical element is a diffractive grating with diffractive structures, such as slits, holes, and modulation index of refraction. A holographic optical element can replace a number of optical components in an imaging system, such as lenses, mirrors, beam splitters, beam combiners, optical filters, and prisms. Using holographic optical elements with light valves enables more compact and portable imaging systems than imaging systems using traditional optics with solid-state and/or narrow-banded illuminators. Most of the existing holographic approaches, however, do not provide a manufacturable method or an effective manufacturable method for fabricating and assembling holographic optical elements with light valves for use in imaging systems.